Fail to ping OpenCR when connected to multiple MX28 servos

[ridethepig]

Hello, our team is trying to use OpenCR as the power supplier for our robot (just like OP3). Something was wrong when connecting multiple MX28 servos to the board.

Here's how we connect them:

• 12V battery to OpenCR
• U2D2 between OpenCR and Laptop (using 3 pin TTL)
• MX28 motors to OpenCR (using 3 pin TTL) without standalone power supply to the motors

Here's what we see:

• With no MX28 motor connected to OpenCR, we can ping OpenCR successfully
• With one or two MX28 motors connected to OpenCR, we can ping OpenCR and manipulate the motors after enabling power to dxl (by writing to OpenCR's control table)
• With 3 or more MX28 motors, we cannot ping OpenCR

We are here to ask for your help, thanks a lot.

We have done something that may be helpful:

We try to find out how this happens, and measured the signals on the wire when pinging OpenCR. We found that the signal's voltage decreased when connecting more motors to the board. (down to about 2V which is not enough for TTL communication)

[ROBOTIS-Will]

Hi @ridethepig

I'm sorry about the delayed response. Please understand that we are unable to provide in-depth technical supports on personal projects.

If your custom OpenCR firmware reads from and writes to MX-28 frequently, you may not have enough time for reading from OpenCR via U2D2. You should consider a proper timing to communicate with OpenCR.

Regarding the voltage drop on TTL line, please make sure that the total length of your TTL channel is within 50 cm and your cable and connectors are in good condition. When the connector terminal is worn out, it may have higher resistance than the new one which may cause voltage drop.

Thank you.

[ridethepig]

Anyways, gratitude.